The advent of the longcase clock is due to the invention of the anchor escapement mechanism around 1670. Prior to that, pendulum clock movements used an older verge escapement mechanism, which required very wide pendulum swings of about 100°.[1] Pendulum panjang dengan ayunan lebar semacam iyu tidak dapat dimuatkan dengan sebuah peti, jadi kebanyakan jam mempunyai pendulum pendek. Mekanisme anchor mengurangkan ayunan pendulum ke sekurangnya 4° to 6°,[1] allowing clockmakers to use longer pendulums, which had slower "beats". These needed less power to keep going, caused less friction and wear in the movement, and were more accurate.[1] Most longcase clocks use a "seconds" (or "Royal"[2]) pendulum, meaning that each swing takes one second. These are about a metre (39 inches) long (to the centre of the bob). This requirement for height, along with the need for a long drop space for the weights which power the clock,[3] gave rise to the design of the long narrow case.

Modern longcase clocks use a more accurate variation of the anchor escapement called the deadbeat escapement.

Most of a longcase clock's height is used to hold the long pendulum and weights. The two chains attached to the weights and the lack of winding holes in the dial show this to be a 30-hour clock.

Traditionally, longcase clocks were made with two types of movement: eight-day and one-day (30-hour) movements. A clock with an eight-day movement required winding only once a week, while generally less expensive 30-hour clocks had to be wound every day. Eight-day clocks are often driven by two weights - one driving the pendulum and the other the striking mechanism, which usually consisted of a bell or chimes. Such movements usually have two keyholes on either side of the dial to wind each one (as can be seen in the Thomas Ross clock above). By contrast, 30-hour clocks often had a single weight to drive both the timekeeping and striking mechanisms. Some 30-hour clocks were made with false keyholes, for customers who wished that guests to their home would think that the household was able to afford the more expensive eight-day clock. All modern striking longcase clocks have eight-day movements. Most longcase clocks are cable-driven, meaning that the weights are suspended by cables. If the cable was attached directly to the weight, the load would cause rotation and untwist the cable strands, so the cable wraps around a pulley mounted to the top of each weight. The mechanical advantage of this arrangement also doubles the running time allowed by a given weight drop.

Cable clocks are wound by inserting a special crank (called a "key") into holes in the clock's face and turning it. Others, however, are chain-driven, meaning that the weights are suspended by chains that wrap around gears in the clock's mechanism, with the other end of the chain hanging down next to the weight. To wind a chain-driven longcase clock, one pulls on the end of each chain, lifting the weights until the weights come up to just under the clock's face.